Chapter 6 Evolution of GSM and cdmaOne to 3G Systems. Chapter 6 Evolution of GSM and cdmaOne to 3G Systems 6.1 Introduction The previous chapters have concentrated on the two leading second generation (2G) cellular systems: GSM and IS-95. These systems are deployed in many parts of the world and will continue to operate and evolve during the next decade as third generation (3G) systems are rolled out. We may expect that the new 3G systems will be harmonised with their evolved 2G counterparts, and that slowly 2G spectra will be refarmed to provide extra 3G spectra. No 3G systems are currently deployed, although trials are in progress. As a consequence, this chapter, which deals with systems that are about to be deployed, is treated in a qual- itative manner, describing how they will work rather than quantifying their performances. Before getting into detail, let us briefly review how cellular communications arrived at to- day’s position. 6.1.1 The generation game There is no doubt that there was pent-up demand for public mobile telephony networks, and when they arrived in the 1980s as the so-called first generation (1G) analogue cellular networks, they grew at phenomenal rates. These networks initially offered only telephony, but the un-tethering of people from their fixed phones meant that they and businesses could operate in completely new ways. The Europeans identified in the early 1980s the need for a second generation (2G) cellular system that would be totally digital. This 2G system became GSM, and a brief history of GSM has already been provided in Section 2.1. The Europeans have a long view in cellular radio and in 1988 they launched their RACE 1043 project with 404 GSM, cdmaOne and 3G Systems. Raymond Steele, Chin-Chun Lee and Peter Gould Copyright © 2001 John Wiley & Sons Ltd Print ISBN 0-471-49185-3 Electronic ISBN 0-470-84167-2 6.1. INTRODUCTION 405 the aim of identifying the services and technologies for an advanced third generation (3G) system for deployment by the year 2000 [1, 2]. Their 3G system soon became known as the universal mobile telecommunications system (UMTS) [3–5]. The concept was that their 1G, 2G and 3G systems would be independent, and that their deployment would overlap such that the total access communications system (TACS), say, would slowly be replaced by GSM, which in turn would be slowly phased out for UMTS. However, the success of GSM has been so great that evolutionary paths from 2G to 3G needed to be considered. Although the back-haul networks of GSM and UMTS have considerable commonality, their radio interfaces are significantly different. There were initially great expectations for UMTS [5,6]. It would not only be cellular, but it would embrace other types of networks from private mobile radio (PMR) (called special mobile radio (SMR) in the United States), to wireless local area networks (WLANs), to mobile satellite systems (MSSs). The cardinal points were that it would operate globally, support high bit rate services and, most importantly, be service orientated. While the Eu- ropeans referred to the global 3G network for the turn of the century as UMTS, most of their engineers working on UMTS expected that they would have to yield to international agreements from the ITU to modify UMTS, but that basically UMTS would be accepted as the global standard. To explain this early expectation we need to point out that the ITU has been in the 3G game from the beginning [6]. Paralleling the European Union (EU) RACE initiative, ITU formed task group TG8/1, originally under the auspices of CCIR. This committee referred to their 3G system as the future public land mobile telecommunications system (FPLMTS). Europeans were, of course, also members of TG8/1, and with commercial and political pres- sures a long way in the future, FPLMTS and UMTS seemed synonymous in terms of aims and objectives. The important difference between TG8/1 and the happenings in Europe, was that in Europe there was an actual research and development (R&D) 3G programme in process, while TG8/1 was more like a forum. The Americans did not launch concerted national R&D programmes, neither for 2G nor 3G systems. Their advanced mobile phone service (AMPS) 1G system did evolve into the 2G IS-136, and became dual-mode with IS-95. The United States also introduced the iDEN system with its ability to offer both cellular and dispatch services. It then auctioned a large part of its 3G spectrum for PCS licenses, and allowed GSM to enter the United States in the form of PCS1900. This auctioning of the 3G spectrum meant that there were significant advantages if existing 2G networks could evolve into 3G ones, preferably in a seamless manner. A big factor, not just in the United States, but in the world, was the advent of IS-95 [7–11]. It arrived late compared with GSM, and some engineers argued that it was a 2.5G system. It had to fight to be born because of the lack of spectrum, and the quasi-religious attitudes 406 CHAPTER 6. EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS of engineers towards methods of multiple access. The meagre spectrum of 1.25 MHz at the top of the AMPS band was just about adequate for cellular CDMA, which was just as well because that was all there was available. CDMA entered the cellular world with a host of technical problems, not made easier as the transceivers from day one had to be dual-mode with AMPS. Its advocates were clear in that CDMA has a high spectral efficiency and is well suited to the 3G multiservice environment. The real significance of IS-95 is that it won the technical argument in that the UMTS and the Japanese Association of Radio Industries and Businesses (ARIB) proposals have CDMA radio interfaces, albeit of wider bandwidth systems as more bandwidth is available for 3G networks. We therefore agree that IS-95 is a 2.5G system and its evolution to 3G should be smooth. This is not so for 2G TDMA systems which will need to migrate to 3G CDMA ones. However, as we will show in Section 6.2, GSM with its TDMA is able to evolve closely to 3G without picking up the CDMA card. Nevertheless there is an evolutionary route from GSM Phase 2+ to UMTS as discussed in Section 6.2 The TG8/1 Committee discarded the unwieldy FPLMTS name for its 3G system, and replaced it with international mobile telecommunications for the year 2000, or simply IMT- 2000. It then abandoned all hope of the difficult political objective of a single standard, and has instead opted for a family of standards. Each member of the family had to be able to meet a minimum specification. Sixteen proposals were accepted, ten for terrestrial 3G networks, and six for MSSs. The majority of the proposals advocated CDMA as the multiple access method. A degree of harmonisation between the proposals ensued, and at the time of writing the ITU has agreed that the IMT-2000 family will be composed of the following five technologies. IMT DS (Direct Sequence). This is widely known as UTRA FDD and W-CDMA, where UTRA stands for the UMTS Terrestrial Radio Access, and the ‘W’ in W- CDMA means wideband. We will refer to this system here as UTRA FDD. IMT MC (Multicarrier). This system is the 3G version of IS-95 (now called cdmaOne), and is also known as cdma2000. We will use the term cdma2000 as this is its widely used name. IMT TC (Time Code). This is the UTRA TDD, namely the UTRA mode that uses time division duplexing. IMT SC (Single Carrier). This is essentially a particular manifestation of GSM Phase 2+, known as EDGE, standing for Enhanced Data Rates for GSM Evolution. IMT FT (Frequency Time). This is the digitally enhanced cordless telecommunica- tions (DECT) system. 6.2. EVOLUTION OF GSM 407 In the authors’ opinion, the truly 3G systems are the IMT DS, IMT MC and IMT TC systems. 6.1.2 IMT-2000 spectrum The World Administration Radio Congress (WARC) in March 1992 assigned 200 MHz in the 2G frequency band to IMT-2000 for world-wide use [3]. The actual frequency bands are 1885–2025 MHz and 2110–2200 MHz. Unfortunately some parts of these bands are already used for other services. Figure 6.1 shows a diagram of the IMT-2000 spectrum, and the current use of this spectrum in Europe, the United States, and Japan. The IMT-2000 spectrum may be partitioned into seven segments. The frequency of each segment is shown in Table 6.1 Part of Segment 1 is currently used for DECT in Europe, and is also used for PHS, PCS and DECT in other parts of the world. Segment 2 is used at present for PCS and PHS in the United States and Japan, respectively. Segments 3 and 6 form 60 MHz frequency division duplex (FDD) bands. Mobile satellite services (MSS) are in Segments 4 and 7, providing 30 MHz FDD bands. Segment 4 supports the earth-to-space links; while segment 7 provides the space-to-earth links. The 1980–1990 MHz band in Segment 4 is currently used for PCS in the United States. Segments 1, 2 and 5 are unpaired and are suitable for time division duplex (TDD) operation. Segment 5 may be used in the United States for earth-to-space MSS services. 6.2 Evolution of GSM The GSM system was initially designed to carry speech, as well as low speed data. Much has already been discussed regarding speech, so we will concentrate here on data. The user data rate over the radio interface using a single physical channel, i.e. a single timeslot per Table 6.1: IMT-2000 spectrum and its segments (MSS stands for mobile satellite services). Segment Frequency Comment number band (MHz) 1 1885–1900 Unpaired 2 1900–1920 Unpaired 3 1920–1980 Paired with 6 4 1980–2010 MSS paired with 7 5 2010–2025 Unpaired 6 2110–2170 Paired with 3 7 2170–2200 MSS paired with 4 408 CHAPTER 6. EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS 1700 1750 1800 1850 1900 1950 2000 2050 2100 22002150 IMT-2000 IMT-2000 MSS MSS ITU Europe GSM1800 GSM1800 DECT PCS SAT SAT USA PHS SAT SAT Japan Reserved Figure 6.1: IMT-2000 spectrum and the current use of this spectrum in Europe, the United States and Japan. PCS stands for personal communication system, SAT for mobile satellite ser- vices, DECT for digitally enhanced cordless telecommunications, and PHS for personal handyphone system. TDMA frame, was initially 9.6 kb/s. The maximum user data rate available on a single physical channel has since been increased to 14.4 kb/s by reducing the power of the channel coding on the full rate traffic channel by means of code symbol puncturing. Apart from increasing the level of puncturing still further, the other ways to increase the user data rate beyond 14.4 kb/s are either to allow an MS to access more than an one timeslot per TDMA frame or to use a higher level modulation scheme (e.g. quadrature amplitude modulation, QAM) to increase the amount of information that can be transmitted within a single timeslot. Two new services have been introduced as part of GSM Phase 2+ which allow the user data rate to be increased by permitting an MS to access more than one timeslot per TDMA frame. These new services are the high speed circuit switched data (HSCSD) service and the general packet radio service (GPRS). The HSCSD service allows an MS to be allocated a number of timeslots per TDMA frame on a circuit-switched basis, i.e. the MS has exclu- sive use of the allocated resources for the duration of a call [12]. In contrast, GPRS uses packet-orientated connections on the radio interface (and within the network) whereby a user is assigned one, or a number of traffic channels only when a transfer of information is required [13]. The channel is relinquished once the transmission is completed. In the following sections we will describe these two services in more detail. 6.2. EVOLUTION OF GSM 409 The second approach to increasing the user data rate by employing a higher level modu- lation scheme is currently being studied under the Enhanced Data Rates for GSM Evolution (EDGE) project [14]. The basic principle behind EDGE is that the modulation scheme used on the GSM radio interface should be chosen on the basis of the quality of the radio link. A higher level modulation scheme is preferred when the link quality is ‘good’, but the system reverts to a lower level modulation scheme when the link quality becomes ‘poor’. At the time of writing it appears that EDGE will use the existing Gaussian minimum shift keying (GMSK) modulation scheme in poor quality channels and eight-level phase shift keying (8- PSK) in good quality channels. EDGE will also include link adaption functions to allow the MS and BS to assess the link quality and switch between the different types of modulation as necessary. Once developed, the EDGE technology will enhance the range of services offered by GSM. The initial version of the EDGE technology (Phase 1) will be used to enhance the GPRS and HSCSD services, leading to enhanced GPRS (EGPRS) and enhanced circuit- switched data (ECSD). In later releases of EDGE (Phase 2 and beyond) further services will be introduced which utilise the different modulation schemes [14]. In addition to the developments described above, GSM Phase 2+ contains two other im- portant enhancements that have a significant impact on the technology from a radio point of view. In 1993 the European railways, in the form of the Union Internationale des Chemins de Fer (UIC), chose the GSM technology as the basis of all their future mobile radio com- munication systems [15]. This led to the introduction of a number of advanced speech call items (ASCI) which provide the additional functionality required for railways and other private mobile radio (PMR) environments. The three key elements of ASCI are the voice broadcast service (VBS), the voice group call service (VGCS) and the enhanced multi-level precedence and pre-emption (eMLPP) service. The VBS will allow GSM users to broadcast their voice simultaneously to a number of other users in a chosen talk group. A VBS call will only occupy a single down-link channel in each cell within which the call is broadcast and all ‘listening’ MSs will monitor this same channel. VBS calls are simplex in that the call originator is the only person who can speak during the call. Many applications require any member of the talk group to become the talker and this functionality is supported in the VGCS. In this case any member of the talk group may become the ‘talker’ and contention resolution schemes are included to handle situations where more that one user tries to be- come the talker simultaneously. These PMR systems also support a facility to ensure that important calls are successfully completed even at the expense of less important calls. The eMLPP service allows calls to be prioritised and ensures that the most important calls are completed, regardless of the network loading. Another important Phase 2+ item from a radio perspective is the adaptive multi-rate (AMR) speech coder [16]. The deployment of the GSM half-rate (HR) codec has been 410 CHAPTER 6. EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS somewhat limited because of concerns relating to the speech quality, but the enhanced full- rate (EFR) codec is more popular amongst GSM operators. The basic concept behind the AMR technology is that the speech coding rate and the degree of channel coding should be chosen according to the channel quality. For example, in ‘good’ channels a lower rate speech coder can be used in an HR traffic channel thereby increasing the system capacity. However, if the link quality is ‘poor’ FR then a traffic channel will be used and the level of channel coding increased. At the time of writing the candidate AMR codecs have not yet been chosen. 6.2.1 High speed circuit-switched data The HSCSD service [12] is a natural extension of the circuit-switched data services that were supported in earlier versions of GSM. No changes to the physical layer interfaces be- tween the different network elements are required for HSCSD. At the higher layers the MS and the network support the additional functionality required to multiplex and demultiplex a user’s data onto a number of traffic channels for transmission over both the Abis interface and the radio interface. Additional functionality is also included at the radio resource man- agement level to handle the new situation where a number of different traffic channels are associated with the same connection. For example, when an HSCSD user is handed over between two cells, there must be a mechanism to ensure that sufficient traffic channels are available in the new cell before the handover occurs. An HSCSD connection is, however, limited to a single 64 kb/s circuit on the A interface. On call set-up the MS provides information to the network which defines the nature of the HSCSD connection. The multislot class of the MS is used by the network to determine the maximum number of timeslots that may be accessed by the MS, and the amount of time that must be allowed between timeslots, e.g. for the purposes of neighbour cell measurements. This information is used to define the MS’s capabilities for both the HSCSD and GPRS services. The multislot classes are listed in Table 6.2 along with their associated parameters [17]. Multislot MSs can be either type 1 or type 2 and this information is shown in the right- hand column of Table 6.2. Type 2 MSs are required to be able to transmit and receive simultaneously, whereas type 1 MSs are not. The ‘Rx’ and ‘Tx’ columns give the maxi- mum number of receive and transmit timeslots that the MS may occupy per TDMA frame, respectively. The ‘Sum’ column gives the total number of transmit and receive timeslots the MS may access per TDMA frame. For example, for multislot class 12, ‘Sum’ is 5 which means that the maximum number of transmit and receive slots cannot exceed 5. So if we have 3 received slots, then we cannot have more than 2 transmit slots in one TDMA frame. The T ta parameter represents the time required for the MS to make a neighbour cell measurement prior to an up-link transmission. This parameter is not applicable to type 2 6.2. EVOLUTION OF GSM 411 MSs because they are capable of making measurements and transmitting simultaneously. When the MS is not required to make measurements on neighbouring cells, the T tb param- eter defines the minimum number of timeslots that must be allowed between the end of the previous down-link timeslot and the next up-link timeslot, or the time between two con- secutive down-link timeslots that are on different frequencies. In other words, T tb is the amount of time the MS needs to prepare to transmit on the up-link after it has received or transmitted on a different frequency. The T ra parameter is the number of timeslots required by the MS to make a neighbour cell measurement prior to the reception of a down-link burst, whereas the T rb parameter is the number of timeslots required between the previous up-link transmission and the next down-link reception, or the time between two consecutive down-link receptions when the frequency is changed in between receptions. In addition to its multislot class, the MS provides a range of additional information on call set-up to allow the network to determine the most appropriate HSCSD configuration. This infor- mation includes the fixed network user rate, i.e. the data rate that the MS would like to achieve over the fixed network, the channel coding schemes supported by the MS, and the maximum number of traffic channels to be used during the connection. This final param- eter allows the user to control the call cost by limiting the number of traffic channels that will be occupied. The final multislot configuration is chosen by the network based on the MS capabilities and the requirements imposed by the services, e.g. whether neighbour cell measurements are required. The HSCSD service can support both symmetric transmissions, i.e. the same number of up-link and down-link timeslots, or asymmetric transmissions, i.e. more timeslots are allocated in one direction. However, in the case of HSCSD connections, only down-link biased asymmetry is allowed and the up-link timeslot numbers must be a subset of the down-link timeslot numbers. 6.2.2 The general packet radio service Many services do not require a continuous bi-directional flow of user data across the radio interface. To illustrate this, consider the example of a user browsing the Worldwide Web (WWW) on her lap-top computer using a dial-up connection via a cellular network. Once a page of information has been downloaded, there will be a pause in the information flow between the MS and the network as the user reads the information and before more infor- mation is requested. Using circuit-switched connections for ‘bursty’ services of this nature represents an inefficient use of the radio resources because a user will continue to occupy a radio channel for the duration of a call (or browsing session) even though this channel may only be utilised for a small fraction of the time. Inefficiencies of this type can be overcome by carrying these services using packet-orientated connections. The GSM system was initially designed to support only circuit-switched connections at the radio interface level with user data rates of up to 9.6 kb/s. However, the Phase 2+ 412 CHAPTER 6. EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS Table 6.2: The MS multislot classes. Multislot Maximum number of slots Minimum number of slots Type class Rx Tx Sum T ta T tb T ra T rb 111 2 3242 1 221 3 3231 1 322 3 3231 1 431 4 3131 1 522 4 3131 1 632 4 3131 1 733 4 3131 1 841 5 3121 1 932 5 3121 1 10 4 2 5 3 1 2 1 1 11 4 3 5 3 1 2 1 1 12 4 4 5 2 1 2 1 1 13 3 3 NA NA a 3 a 2 14 4 4 NA NA a 3 a 2 15 5 5 NA NA a 3 a 2 16 6 6 NA NA a 2 a 2 17 7 7 NA NA a 1 0 2 18 8 8 NA NA 0 0 0 2 19 6 2 NA 3 b 2 c 1 20 6 3 NA 3 b 2 c 1 21 6 4 NA 3 b 2 c 1 22 6 4 NA 2 b 2 c 1 23 6 6 NA 2 b 2 c 1 24 8 2 NA 3 b 2 c 1 25 8 3 NA 3 b 2 c 1 26 8 4 NA 3 b 2 c 1 27 8 4 NA 2 b 2 c 1 28 8 6 NA 2 b 2 c 1 29 8 8 NA 2 b 2 c 1 NA = Not Applicable a = ( 1 if frequency hopping is used 0 if frequency hopping is not used b = ( 1 if frequency hopping is used or there is a change from Rx to Tx 0 if frequency hopping is not used and there is no change from Rx to Tx c = ( 1 if frequency hopping is used or there is a change from Tx to Rx 0 if frequency hopping is not used and there is no change from Tx to Rx [...]... CHAPTER 6 EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS analyser using a bandwidth of 30 KHz The maximum output power as a function of 4 f between 2.7 and 3.5 MHz must be less than 14 15(4 f 2:7) dBm The darker shaded area of the figure is associated with the right-hand ordinate, which is the power measured in a 1 MHz bandwidth The value of 4 fmax is 12.5 MHz, or the edge of the allotted frequency band for... Signalling Only Modified from 3GPP TS 23.002 Version 3.1.0 Figure 6.5: UMTS network architecture 426 CHAPTER 6 EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS represents circuit-switched The equivalent of the Abis in UMTS is Iubis This figure is important because it illustrates the evolutionary path from GSM Phase2+ to UMTS We see the different radio interfaces of GSM and UMTS plugging into a common backbone network... as and when required Data rates range from 438 CHAPTER 6 EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS Figure 6.16: Slot and frame structure of the primary common control physical channel 30 kb/s to 1920 kb/s, corresponding to spreading factors of 256 to 4, respectively The data rate can be varied as required using the TFCI The S-CCPCH is scrambled by either the primary or secondary scrambling code, and. .. maintenance and release procedures between an MS and the PLMN over the radio interface These functions involve the co-ordination of link state information and the supervision of data activity over the logical link 418 CHAPTER 6 EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS Radio resource management functions Allocation and maintenance of radio communication channels are provided by these functions The GSM radio... modulation was part of the UWC-136 IMT EDGE proposal The evolution of GSM to EDGE and IS-136 to EDGE is now undertaken jointly by ETSI and the UWC Consortium Consequently, EDGE will be compatible with both GSM and IS136 The plan [14] is to deploy GPRS, then enhanced GPRS (EDPRS) and enhanced circuit switch data (ECSD) Then the high level of modulation will be deployed to realise 3G EDGE services EDGE... is not mandatory A SGSN keeps track of the location information and the security information associated with the MSs that are within its service area A SGSN communicates with GGSNs and SGSNs in its own PLMN using the Gn interface and GGSNs in other PLMNs via the Gp interface Interfaces also exist between an SGSN and an MSC/VLR (Gs interface), 414 CHAPTER 6 EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS. .. CDMAONE TO 3G SYSTEMS rate of 0.16, 0.26, 0.53 and 0.64, respectively; while for 8-PSK the bit rates have the higher values of 14.5, 29, 32 and 38.8 kb/s for code rates of 0.42, 0.46, and 0.56, respectively For EGPRS when QoS issues are addressed where different factors, such as priority of packet transmissions, packet delay, packet throughput, maximum and minimum bit rates that must be handled, and so... example of an application that could make use of this facility is automatic road-tolling, whereby a road user could use a pre-paid card, inserted into a GSM terminal, automatically to make payment as she approaches a toll booth Packet routing and transfer functions A route consists of an originating network node, and if required, relay nodes, and finally a destination node Routing is the transmission of. .. centre (MSC), and there is an IuPS between a BSC and SGSN, where the subscript uPS signifies a packet switch interface The Abis interface between a BTS and a BSC is also shown The UMTS network uses the same core network as GSM, and has interfaces between the RNC and MSC, SGSN and RNC of IuCS , IuPS and Iur , respectively The subscript uCS Table 6.4: GSM and UMTS terminologies of some key entities GSM Mobile... the pilot bits are placed between data 2 bits and data 1 bits We also note that, unlike GSM where sounding is executed every 4.6 ms, UTRA sounds the radio channel every 0.667 ms The greater sounding rate of UTRA is necessary because of the higher bit rate services supported by UTRA compared with those in GSM 430 CHAPTER 6 EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS Slot DPDCH Data1 DPCCH TPC DPDCH DPCCH . Chapter 6 Evolution of GSM and cdmaOne to 3G Systems. Chapter 6 Evolution of GSM and cdmaOne to 3G Systems 6.1 Introduction The previous. had to fight to be born because of the lack of spectrum, and the quasi-religious attitudes 406 CHAPTER 6. EVOLUTION OF GSM AND CDMAONE TO 3G SYSTEMS of